Beneficiation of iron ores



Patented Oct. 29, 1946 BENEFICIATION OF IRON ORES Robert B. Booth, Springdale, and Earl C. Herkenhofi, Stamford, Conn., assignors to American Cyanamid Company, New York, N. Y., a corporation of Maine No Drawing. Application June 18, 1943, Serial No. 491,384

6 Claims. (Cl. 209166) This invention relates to an improved method.

of beneficiating iron ore by froth flotation.

The problem of iron ore beneficiation has been a serious one because of the low unit value of the product and the fact that, while it is not difiicult to float various iron minerals, the procedures em- I determinate composition, and it is probable that a considerable proportion of the green acid is in the form of hydrocarbon sulfates rather than true sulfonates, that is to say compounds which have the group SOsH united to a carbon atom. However, it is customary in the industry to refer to these products as petroleum sulfonates of the green acid type, and; therefore, throughout the present specification and claims the term petroleum sulfonates of the green acid type will be used in its common meaning above.

The water solublte petroleum sulfonates are used under definite conditions and the present invention is limited to their use under such conditions and does not cover the use of these reagents generally. According to the present invention the ore must be conditioned with the reagent in the presence of a strong acid. The effectiveness of the acid treatment is not apparently dependent on the nature of the acid anion insofar as it does not have a particular depressant effect and almost any strong or fairly strong acid may be used, either inorganic or organic. The limit of effectiveness appears to lie with acids having an ionization constant of about 10- Thus carbonic acid gives barely acceptable results while weaker acids such as boric acid are not satisfactory. Sulfuric acid gives excellent results and because of its extremely low cost it is the preferred acid. Certain strongly acid salts appear to have some effect and may be used, although in 2 enough, This obviates the necessity of extremely accurate pH control and permits a material saving in operating supervision. Although the pH and the nature of the particular acid is not c'rit-' ical, there will be optimum conditions for each particular acid. Another factor which has not as yet been fully explained is the fact that it is not necessary that the actual froth flotation. take place in a circuit which is strongly acid. On the contrary, if iron ore is conditioned with the hydrocarbon sulfonates and a suitable acid, the pH of the flotation circuit may be modified with alkalies such as soda ash, and, in fact, it is even possible to float in a weakly alkaline circuit. The neutralization appears to have but little effect on the flotation of the acid conditioned ore. This permits, with certain ores, operating practically in a circuit which is not strongly acid, an important commercial advantage because strongly acid circuits require corrosion-proof flotation apparatus, whereas if it is possible to neutralize acid conditioned ore prior to flotation only the conditioning equipment need be made acid proof, This equipment not only represents only a fraction of the total plant, but it is in general of a character which lends itself readily to economical corrosion resistant construction, whereas the flotation machines themselves are more diflicult to build and expensive if they must withstand strongly acid circuits.

Watr soluble petroleum sulfonates and acid alone do not appear 'to give optimum results and we have found that conditioning in the presence of an oil is desirable for best recoveries and grades. It is an advantage of the present invention that the nature of the oil is not particularly critical. Excellent results are obtained with various hydrocarbon products such as various grades of fuel oil or even crude oil. Since these oils are among the cheapest commercially available materials they may be considered as the preferred oils to be used in the process of the present invention. However, other oily materials are effective such as certain fatty acids, mixtures of fatty and resin acids such as talloel, esters of monohydric alcohols and the like. Esters of glycerin, while effective, appear to give results which are in most cases inferior to the other oils and, while their use is not critical, for best results we prefer to use other oils.

Conditioning and flotation procedure is not materially changed by the present invention, which is a further practical advantage as no new operating technique need to be learned. It is desirable to condition the ore with the flotation reagents at high solids, for example from 50-70% which is standard practice in many flotation operations, particularly those involving reagents containing relatively insoluble oils such as fuel oil. Thus, the procedure is standard in the flotation of phosphate rock with fatty acids and fuel oil. Well known conditioning equipment 3 may, therefore, be used and special apparatus is unnecessary except to the extent that the conditioning apparatus at least must be corrosion proof.

It is an advantage of the processof the present invention that it is not highly sensitive to slimes. In common with almost all froth flotation operations slimes are a detriment. but in the process of the present invention desliming need not be carried to completion, and relatively simple and hence economical desliming operations are quite suitable. It is not necessary to deslime to the completeness which is required with froth flotation operations using cationic reagents. The

action of the slime appears to be a normal or usual one, that is to say the presence of small amounts of slime increase the amount of reagent needed for best results, .and when the amount of similar to the action in other froth flotation procedures.

The lack of sensitiveness to small amounts of slime is of considerable practical value, as the feed preparation need not he so .closely controlled and the cost of desliming equip- .ment may be reduced.

It is an important advantage of the process of the present invention that it is applicable to practicallyall of the ordinary occurring iron minerals and is not restricted to certain particular ores. As in the case of most froth flotation operations, however, results will differ with different ores. It is an advantage, however, that concentrates of acceptable grade may be produced from low grade ore having iron contents of the order of 12 or 13%. It is also an advantage that the process is so highly selective that in many casesconcentrates of satisfactory grade are obtainable in a rougher operation- However, with many ores, and particularly with many low grade ores, cleaning is advantageous, and in common with froth flotation experience on other ores the precise flow sheet for best results will vary somewhat from ore to ore and should be chosen in accordancewith best ore dressing practice. The lack of criticalness of the present process, however, makes the choice of plant and procedure simple and no .operating 'difliculties are encountered.

The process of the present invention may be carried out'in any suitable flotation machine. Where high outputs are needed, particularly with relatively coarse .ore, we have found that the use of highly developed flotation machines of the mechanical type such as Fagergren flotation machines are desirable, but the invention is not limin the fact that it is not peculiarly susceptible to temperature and can be operated with very cold water. This is of real practical advantage because much of the low grade iron ore for which the present invention is suitable lies in the northern part of the United States where low water temperatures are the rule at the beginning and end of the short mining season.

The process of the present invention may be used with water soluble petroleum sulfonates as the only reagent except for the conditioning acid and oil. It is also possible to associate these reagents with other flotation reagents. For example, mixtures of the water-soluble petroleum sulfonates with oil-soluble petroleum sulfonates, such as the so-called mahogany soaps, give ex- V cellent results. The use of oil soluble petroleum sulfonates is not claimed per se in the present invention, but forms the subject matter of our co-pending application, Serial No. 481,906, filed April 5, 1943. j

The invention will be described in greater detail in conjunction with the following specific examples. In the examples the froth flotation procedure was standardized. All flotation was effected in Fagergren flotation machines operating at normal speeds and with normal air intake. Flotation time was chosen in each case to obtain good results. In every case the conditioning of the ore with water soluble petroleum sulfonate and acid was effected at high solids, usually about -65%.

The petroleum sulfonates of the present invention include the products of reaction of sulfuric acid or oleum with various petroleum lubricating oil fractions. They do not, however, include reaction products of the acid with derivatives such as cracking still gases containing ethylene, propylene and similar molecular gaseous olefines, or light unrefined fuel stocks, such as kerosene fractions.

Example 1 A low gradeMinnesota iron ore, a reject from an iron beneflciation operation, containing iron largely in the form of hematite with,a small amount of limonite, having a gangue high in quarts and containing about 15% Fe was deslimed in the conventional manner, and conditioned at 60-65% solids with various combinations of water soluble petroleum sulfonates with and without sulfuric acid. The conditioned ore was then diluted to flotation density, about 22% solids, and subjected to froth flotation with a single cleaning, except in certain cases where no sulfuric acid was used and the rougher concentrate was obviously too small to be worth cleaning. The metallurgical results appear in the following table:

Concentrate, Sulfonate used Lbs/ton percent Fe pH of F l S lf D t 'b tunings no u uric 15 n u Source N ame Lbs/ton oil acid Assay tion L. Sonneborn Sons Inc 2. 18 None None 62. 55 19. 6. 5 D 2.18 None 1. 63 61. 97 43. 00 2. 5 2. l8 0. 94 None 60. 35 40. D1 6. 5 2. l8 0. 51 1. (i3 60. 33 92. 28 2. 5 2. 18 None None 55. 08 16. 76 6. (i 2. 18 1. 22 None 49. 23. 78 6. 6 2. 18 None 1. 63 55. 08 58. 28 2. 8 2. l8 1. 22 1. 63 57. 53 78. 42 2. 8 3. 27 3. 59 None 59. 05 79. 61 2. 6 3. 27 3. 59 1. 63 56. 83 83. 68 2. 4 2. l8 3. 59 None 46. 10 18. 63 6. 5 Do l 2.18 3. 59 1. 63 '60. 57 79. 56 2. 7 (111 Pout 2. l4 5. 07 1. 63 60. 00 63. 54 2. 6

1 Contained about 88% sulfonic acids, 10% sulfuric acid, and traces of oil.

Concentrate per- Lbs.lton

- cent Fe Rougher tailliiig Soda Distri- P H2804 Ash Assay bution 5. 45 None 60. 92 47. 47 2. 1

2. 72 None 61. 38 40. 02 2. 4

1. 63 None 61. 97 43. 2. 6

O. 54 None 61. 38 56. 37 3.0 None None 62. 55 19.70 6. None 0. 54 61. 62 30. 93 8. 5 None 3. 60 61. 82 10. 88 10. 1

It will be apparent that optimum results are obtainable at a pH of about 3 and that when no acid is used the results drop off sharply.

Example 3 The ore and procedure were the same as in Exampl 1, except for the pulp density in conditioning. Two densities were used, 65% solids and 22% solids. In each case the amount of green acids was 2.18 lbs. per ton. 0.51 lb. per ton of 22 B. fuel oil was used with 1.63 lbs. per ton of sulfuric acid. The results appear in the following table:

Concentrate, Pulp density per cent Fe Taflmg per cent solids Assay .Condi- Distri- Flota- Assa er cent H tiony bution p Fe p mg tlon Example 4 The procedure of Example 1 was followed using 2.18 lbs..pe r ton of a water soluble petroleum sulfonate, SP-702, with varying amounts of fuel oil. The metallurgical results appear in the following table:

Concentrate Lbslton Feed per cent Fe assay.t Fuel per cen H 8 04 Neal] 2 0 Assay 2 None 1. 22 13. 07 49. 95 23. 78 1. 63 N011!) 12. 78 55. O8 58. 28 1. 63 0. 61 12. 72 57. 07 84. 88 1. 63 1. 22 12. 62 57. 53 78. 42 1. 63 1. 83 12. 59 58. 23 74. 06

It will be apparent that there is an optimum amount of fuel oil, which for this particular ore and petroleum sulfonate was about 0.6 pound.

Example 5 v Ore of Example 1 was conditioned at high solids with 2.18 lbs. per ton of water soluble petroleum sulfonate, using SP-702 for the first 13 tests and Sonesal (green acids) for all the remainder but the last test. In the last test 2.18 lbs/ton of a 1:1 mixture of'SP-702 andSonesal was used.

The amount of sulfuric acid in every case was 1.63 lbs. per ton. In all cases a rougher concentrate was removed and cleaned once. The different tests were made with different oils. The metallurgical results appear in the following table:

Addition reagent pe/rcent Type Lbs/ton Assay Distribution None 55. O8 58. 28 Oleic acid 0.78 56. 72 90. 39 Coconut 011. 0.55 61.62 43. 39 Crude oil 0. 76 53. 57 92. 69 Chlorinated kerosene 0.76 59. 52 81. 04 Talloel 0. 82 57. 18 91. 50 Cottonseed oil 0. 27 59. 87 50.09 Nabhthenic acid 0. 77 54. 85 75. 51 n-Heptaldehyde 0. 75 56. 25 70. 15 Fuel oil No. 2 0. 61 57.07 84. 88 Methyl ester of talloel. l. 00 60. 45 75.04 Saponified talloeL. 0. 82 51. 00 84. 17 Barrett No. 4 0. 76 50.88 71. 80

None 61. 97 43. 00 Crude oil l 0.76 59. 63 .94. 07 Lubricating oil (IO-W) 0. 80 60. 68 75. 75 Methvi ester of talluel--- 0.78 59. 05 89.85 Bunker C" fuel 0il. 0.76 59. 75 93. 29 Chlorinated kerosene 0.84 60. 45 86.70 Coconut oil 0. 61. 38 63. n-Heptaldehydc. O. 71 60. 33 80. 34 Naphthenic acid. 0. 77 50.30 92. 74 Lauryl mercaptan 0. 69 60. 45 77. 28 22 B. fl1e101l-- 0. 51 60. 33 92. 28 Fuel oil No 2 l. 22 58. 23 83. 73 Talloel 0. 82 54. 50 91. 81

Talloel 0. 82 65. 78 93. 60

1 Tim this test 2.18 lbs. of a 1:1 mixture of SP-702 and green acid was use Example 6 Concentrate, Acidic material used per cent Fe Tailing D t pH is r1- Type Lbs/ton Assay bution Hydrochloric acid 1. 63 51. 93. 84 2. Nitric acid 1. 63 53. 10 94. 50 2. Hydrofluoric acid 1. 63 53. 92 94. 44 3. Hydrofluorsilicic ac d 4. 30 53. 8O 90. 72 3. 5. 45 54. 73 61. 7. 2. 72 50.18 91. 62 2. 2. 30 48. 20 92. 89 2. Phosphoric acid 2. 70 50.65 90. 66 2. Sulfnrous acid. 4. 00 55. 20 96. 49 3. Sulfuric acid. 1. 63 53. 95 93. 68 2. Carbonic acid. 45. 86 79. 41 5. Chlorine 49. 48 89. 70 2. B23 Saturated 49. 71 64. 54 6. Hydrobromic acid (1.03

lbs/ton fuel oil) 1.34 41. 38 94. 82 3. Weak oil refinery acid 5. 23 51. 58 91. 20 2. Formic acid 3. 27 46. 91 96.02 3. Acetic acid" 2. 72 50.18 95. 27 4. Acrylic acid. 3. 60 43. 30 96. 12. 3. Oxalic acid.. 2. 72 51. 23 81. 31 2. Lactic acid. 3. 27 43. 88 96. 17 3. Tartaric acid 3.27 51.11 95. 3. Citric acid 2. 72 53. 92 93. 99 3. Maleic anhydride 3. 27 44. 58 95. 54 2. Tricarballylic acid 3. 60 45. 74 94.76 3. Benzoic acid 3. 27 29. 53 87. 57 3. Phthalic acid 3. 82 44. 22 S9. 81 3. Salicylic acid (1.03 lbs./

ton fuel oil) 2. 73 35. 83 91. 57 3. p.'loluene sulfonic acid. 2.18 50.06 95. 89 3. Phenol (1.03 lbs/ton fuel oil) 4. 36 47.06 61. 94 7.

l Contained about 48% H 804.

It will be apparent that all of the stronger acids work satisfactorily and good results are obtained 7 down to acids having an ionization constant of 10*". It should be noted that the somewhat lower grade of concentrate is due to the fact that in the above example there was no cleaning, the

It will be noted that .the presence of slime'required an increase in the amounts of reagents for best results, the increase in the amount of fuel oil needed being particularly striking with data being on rougher flotation alone. For this the undeslimed ore. At the same time it will be particular ore cleaning is of importance to obtain noted that excellent grades were obtainable with concentrates of commercial grade. good recovery for partially deslimed ore as well Example 7 as for completelydeslimed ore, the latter showing only a slight improvement in grade but per- The procedure of Example 1 was followed, but mitting the use of materially reduced amounts acid salts instead of free acids were used. The of reagent. In common with usual flotation pracmetallurgical results appear in the following tatice, operation on completely undeslimed ore was ble: much less economical.

Green acids Acidic Salt used LbsJton concenmgg per cent i s used 0 B. al 111,, lbs/ton fuel 011 PH Type Lbs/ton Assay Distribution 3. 27 Potassium bisulfate... 10.9 1.00 55.90 85. 2.2 2.18 Sodium chlorosulfonate. 5.45 0. 52 59.87 79.39 2.6

Example 8 ExampZe 9 A sample of the ore of Example 1 wasdivided In order to determine the effects of the reinto three parts. One portion was not deslimed agents of the present invention on various iron at all. A second portion was partially deslimed,

using ordinary desliming procedures, and the and the partially deslimed and undeslimed material was cleaned twice. The metallurgical results appear in the following table, in which the minerals present in ores, the pure minerals were ground to -100 mesh, +325 mesh and deslimed prior to flotation. They were conditioned with green acids, fuel oil, and sulfuric acid (in each case there was a blank with no acid, except in the case of goethite), and were floated in a laboratory Fager'gren flotation machine. As the minerals are pure, the efficiency of flotation is measured by the percent of material floated. The results appear in the following table:

Reagents, lbs/ton weight grams Per cent Mineral No 2 Green pH floated H2504 fuel acids Feed Float Tail Magnetlte 8. 0. 75 '1. 0 2. 5 30. 6 27. 1 3. 5 88. 6 D None 0. 75 1.0 7. 1 30.5 0. 7 29. 8 2.3 Titaniferous magname 0. 75 1. 0 2. a 30.1 24.6 5. 5 s1. 7 0. 75 1. 0 6. 9 30. 2 1. 2 29. 0 4. 0 1. 5. 0 2. 5 33. 6 32. 2 l. 4 95. 8 1. 50 5. 0 6. 6 32. 7 14. 8 17. 9 45. 3 1. 50 5. 0 2. 2 29. 4 29. 3 0. 1 99. 7 0. 75 1. 0 2. 4 29. 4 27.1 2. 3 92. 2 0. 75 1.0 6. 9 29. 9 l. l 28. 8 3. 7 3. 00 5. 0 2. 9 30. 8 20. 1 10. 7 65. 3 3. 00 5. O 6. 8 30. 4 1. 4 29. 0 4. 6 0. 75 1. 0 3. 3 31. 3 30. 8 O. 5 98. 5 0. 75 1. 0 6. 6 30. 9 20. 3 10. 6 65. 7 O. 75 l. 0 2.1 31. 7 31. 5 0. 2 99. 4 0. 75 1. O 6. 4 31. 3 5. 7 25. 6 18. 2

first test is on completely deslimed, the second Erample 10 on partially deslimed, and the third on undeslimed ore:

An iron ore of Example 1 was conditioned with mixtures of water soluble petroleum sulfonates Assay Per cent Lbs/ton used Product K525i Fe distri- Per cent Per cent bution Green HS 0 Fuel e msol. acids 2 4 il 100. 00 14. 73 100. 00 8. 19 28. 96 16. 1O 18. 33 59. 34 73. 82 3. 80 6. 62 l. 71 R311. tail 69. 68 l. 77 8.37

Head 100. 00 14. 92 100. 00 Slime 3. 42 '37. 94 8. 70 Clean cone- 18. 74 58. 75 73. 78 2nd clean. tail... 1.13 30. 02 2. 27 1st clean. tail 3. 35 10. 99 2.47 Rgh. tail 73. 36 2. 60 12. 78

.Hcad 100. O0 14. 60 100. 00

Clean. 0on0 24. 87 51. 77 88. 18 2. 72 2. 18 2nd clean. tail"- 3. 56 16. 08 3. 92 1st clean. tail 5.09 5. 67 1.98 Rgh. tail 66. 48 l. 30 5. 92

and various types of mahogany soaps Or oil soluble petroleum sulfonates. Conditionin was at high solids and in every case 1.63 lbs. per ton of sulfuric acid were used. The amount of green acids was 1.09 lbs. per ton. In all but one of the tests there was no additional fuel oil. The floats are rougher floats only. The metallurgical results appear in the following table:

The procedure of Example 1 was followed but the ore was first deslimed, then scrubbed or polished by agitation in a flotation cell with the air shut off at 25% solids, and thenagain deslimed to remove secondary slimes. Conditioning was with 1.63 lbs. per ton of sulfuric acid, 1.09 lbs. per ton green acids, and 0.51 lb. per ton 22 B. fuel oil. Two cleaning floats were conducted. The metallurgical results appear in the following table:

Per cent Per cent Per cent Per cent Pmduct weight Fe insol. fg gg Head 100. 100.00 Prim. slime 6. 14 14. 83 Sec. slime..- 2. 40 6. 61 Clean. conc 17. 15 70. 70 Comb. clean. tails 11. 49 3. 79 Rgh. tail 62.82 4.07

The results should be compared with the completely deslimed ore of Example 8. It will be noted that the grade is slightly higher, the recovery almost as good, and the amount of reagent halved. In many cases the saving in reagent obtainable by scrubbing is commercially worthwhile.

Example 12 The ore of Example 1 was deslimed, conditioned at 67% solids with 2.18 lbs. per ton green acids, 1.63 lbs. per ton sulfuric acid and 0.51 lb. per ton 22 Be. fuel oil. The conditioned ore was then diluted to 22% solids and floated in a Fagergren flotation machine. The concentrate was then conditioned at about 6% solids with 2.18 lbs. per ton of soda ash and 1.63 lbs. per ton of quebracho. The conditioned ore was then deslimed and subjected to cationic flotation in a Fagergren flotation cell, using as reagents 0.12 lb. per ton pine oil and 0.22 lb. per ton laurylamine hydro- 10 chloride. The metallurgical results of the double float appear in the following table:

The procedure of Example 1 was followed, using 2.18 lbs. per ton green acids and, 1.63 lbs. per ton sulfuric acid, except in the case of the sixth test of the first table. This sixth test was a blank test and no sulfuric acid was used. The pulp was then diluted to flotation density and varying amounts of alkali were used to neutralize partly or wholly the acidity. Flotation was then effected and the metallurgical results appear in the following tables, in which the first shows various amounts of soda ash, including the blank test, and the second table shows the effect of various types of alkali: 7

Concentrate, per cent R h e oug er ig Z21 1 tailing D Assay Distribution None 60. 33 92. 28 2. 5 .54 57 88 88.25 2.7 l. 63 57. 53 90. 25 5. 9 2. 18 59. 57 88. 71 7. l 8. 60 58.86 86. 25 8.0 3. 60 61. 82 10. 88 10. 1

. Concentrate per Alkali used cent Fe Rougher tilllllilg Distribu- 9 Type Lbs/ton Assay on Calcium carbonate l. 0 56. 28 87. 64 3. 5 Hydrated lime 1.0 57. 94 87.06 6. 8 Caustic soda 1. 0 59.00 86. 61 6. 3 Ammonia 0.83 56. 76 87.03 8. 6

It will be apparent that there is but little loss in efficiency when the acid conditioned material is neutralized with alkali.

Exampl 14 The effect of the process of the present invention on various iron ores was tested. In each case the ore was ground, if necessary, deslimed, conditioned at 60-65% solids, diluted to flotation pulp density and floated in a Fagergren flotation machine. Cleanin was effected once, except with the tests marked with an asterisk, where the recleaning was used. In every case the reagent combination giving best results was employed. The metallurgical results appear in the following table:

Lbs/ton Concentrate,

Feed per cent Fe Rougher Source of ore fi ggfi tailing Green 22 B6 p Fe DistripH acids fuel oil Assay bution 1 2. 72 1. 63 0. 76 Minnesota (a washer reject) 30. 47 58. 63 92. 66 2.6

1. 50 2.00 0. 70 New Jersey (a table product) 64. 77 69. 29 95. 87 2.9

1 1. 63 1. 63 0. Minnesota (classifier overflow) 13. 72 53. 21 85.60 2. 5

3. 10 1. 93 0.90 Minnesota (a taconite 23. 16 59.10 93.76 2. 6

l Cleaned twice.

It will be apparent that in the case of all of the ores commercially useful results were obtained except with two very refractory Minnesota ores and a Canadian ore, where the grade was slightly below the present specifications for concentrate. In the case of these ores the difiiculty was not due to" the efiiciency of the flotation but because the ore was highly refractory, containing gangue and iron locked together even in very fine sizes.

All of the petroleum sulfonates referred to in the examples under their trade names are typical petroleum sulfonates of the green acid type or, in the case of Example 10, green acid or mahogany acid type, as commercially obtained from the treatment of petroleum lubricating oil fractions with sulfonating agents, such as sulfuric acid, oleum, and the like.

We claim:

1. A method of beneficiating oxidized iron ores by froth flotation which comprises conditioning theore at high solids with an acid substance, the anion of which is a constituent of an acid having a dissociation constant not less than 10*, and which does not adversely affect flotation, an unsulfonated oil, and a collector for oxidized iron minerals containing as its major active constituent water soluble petroleum sulfonates of the green acid type obtained in the refining of petroleum lubricating oils, diluting the thus conditioned pulp to froth flotation density, subjecting it to froth flotation to produce a concentrate relatively rich in iron and a tailing relatively poor in iron, the amount of the acid substance being sufficient so that, in the absence of added alkali,

the pH of the rougher tailing is in the range of Zto 6. I r

2'. A method of beneficiating oxidized iron ores by froth flotation which comprises conditioning the ore at high solids with sulfuric acid, and unsulfonated oil, anda collector for oxidized iron minerals containing as its major active constituent water soluble petroleum sulfonates of the green acid type obtained in the refining of petroleum lubricating oils, diluting the thus conditioned pulp to froth flotation density, subjecting it to froth flotation to produce a concentrate relatively rich in iron and a tailing relatively poor in iron, the amount of the sulfuric acid being sufficient so that in the absence of added alkali, the pH of the rougher tailings is in the range of 3. A method according to claim 1 in which th unsulfonated oil is a petroleum hydrocarbon oil.

4. A method according to claim 2 in which the unsulfonated oil is a petroleum hydrocarbon oil.

5. A method according to claim 1 in which the ore pulp is conditioned at high solids with the acid, collector and oil, diluted to flotation pulp density and subjected to froth flotation after substantial neutralization of the acid by means of an alkali.

6. A method according to claim 2 in which the ore pulp is conditioned at high solids with the acid collector and oil, diluted to flotation pulp density and subjected to froth flotation after substantial neutralization of the acid by means of an alkali.

ROBERT B. BOOTH. EARL C. HERKENHOFF. 

